1. Field of the Invention
The present invention relates to a semiconductor fabrication apparatus used for cleaning semiconductor wafers, and more particularly, this invention relates to a wafer drying apparatus for drying semiconductor wafers after cleaning them.
2. Description of the Related Art
The high degree of integration in semiconductor devices has necessitated the development of a variety of wafer cleaning techniques, which are very important in the field of semiconductor fabrication. Since, in fabricating semiconductor devices with highly integrated and fine configurations, contamination materials such as, particles remaining on the wafers after cleaning, electrostatic discharge, and water marks or the like, all exert an undesirable influence on subsequent process steps. A wafer drying process is thus required to eliminate the contamination materials.
In recent years, the apparatus for drying wafers have included: (1) spin dryers, and (2) a drying apparatus using isopropyl alcohol (IPA). The first apparatus drys the wafers by using centrifugal force. The second apparatus drys the wafers by using a low vapor pressure of isopropyl alcohol (hereinafter, referred to as "IPA").
The spin dryer has serious problems in that the wafers may be broken due to the mechanical force of the drying technique, and/or the wafers may not be sufficiently dried as a result of the highly integrated and fine structure of the semiconductor device. Accordingly, the conventional process using IPA for drying (hereinafter, referred to as "IPA dryer") is frequently used for cleaning wafers. Such a conventional IPA dryer is shown in FIG. 1.
The conventional IPA dryer comprises a process chamber 10 in which wafers 15 are dried for about 5 to 10 minutes by IPA solution 11. The IPA solution 11 is introduced in the process chamber 10 through a supply line (not shown). In the conventional IPA dryer, the wafers 15 in a wafer carrier 14 are located in the process chamber 10 and dried by IPA vapor. The IPA vapor is produced by heating the IPA solution 11 supplied in the process chamber 10 by means of a heater 16.
After the completion of the drying process in the process chamber 10, the IPA solution 11 remaining on the bottom of the chamber 10 is exhausted through an exhaust valve 13b, which is in turn connected to an exhaust line 13. The exhausted IPA solution is collected in a collecting tank (not shown). At the same time, residual products including condensed IPA vapor on the condensed vapor collecting plate 12 are exhausted through the exhaust valve 13a into the collecting tank. Reference numeral 17 in FIG. 1 represents a cooling line, which is provided to prevent the condensed IPA vapor at the top of the process chamber 10 from being exhausted outside.
When the wafer drying process is completed using the IPA vapor, the wafer carrier 14 is transported from the process chamber 10 to the outside of the chamber. The wafers in the carrier 14 are then dried in the ambient atmosphere at room temperature. With such a drying process, a problem arises in that gelled particles are continuously formed on the wafers and at the edges of the wafers. This is because the structure of the vapor zone surrounding the wafers is deformed. This deformation occurs because during repeated drying cycles, the IPA vapor rising toward the top of the process chamber is liquefied in a moment by the cooling line 17 located at the top thereof and is changed back again into IPA vapor by the heater 16. The deformation can also bring about an insufficient process of drying the wafers, which allows particles to remain on them.
In addition, since the drying cycle consisting of supplying an IPA solution into the chamber, thermal treatment, the formation of vapor, and condensation of the vapor, is continuously performed, contamination materials caused by the dryer itself may produce many particles on wafers.
Moreover, in the conventional wafer drying apparatus, since the first drying process in the process chamber 10 is performed at a temperature of about 80.degree. C. and the second drying process is outside of the chamber at a temperature of about 25.degree.C., the IPA vapor adhered to the carrier 14 and the wafers during the first drying process is condensed at a relatively low temperature during the second drying process, and the IPA vapor is liquefied. The liquefied IPA compound reacts to the surrounding air during the second drying process, which can cause different defects on the edge portions of the wafers or on the carrier 14 in contact with the wafers 15.